Enhanced efficacy aluminum and aluminum-zirconium antiperspirant salts are well known and are described, for example, U.S. Pat. Nos. 4,359,456; 4,775,528; 4,859,446, 4,871,525; 4,900,534; 4,944,933; 5,202,115; 5,234,677; 5,296,623; and 5,330,751. These enhanced salts are also known to rapidly revert back to their non-enhanced state in solution, particularly at concentrations greater than 20%. Consequently, the enhanced antiperspirant salts are generally only available in powder form.
A number of references describe various ways of making alcohol soluble antiperspirant actives. These references include, for example, U.S. Pat. Nos. 3,405,153; 3,420,932; 3,523,130; and 3,947,556. In each case concentrated solutions of the antiperspirant active (i.e., in the 40 to 50% range) are employed as a starting material and the product is obtained as a powder, which must then be redissolved in the desired alcohol solution. Such techniques pre-date the availability of enhanced efficacy salts and are not believed to be applicable thereto as they would likely cause reversion to the non-enhanced state. An alcohol soluble complex of aluminum chlorohydrate and propylene glycol may be prepared by spray drying a propylene glycol solution of the aluminum chlorohydrate.
Two methods of making polyhydric alcohol solutions of antiperspirant salts have been described. In one method a powdered antiperspirant salt, which may be an enhanced efficacy salt, is dissolved directly in a polyhydric alcohol, such as propylene glycol. In the other case, the polyhydric alcohol contains about 10 to 20% water and the antiperspirant salt has a water content greater than 10%.
A method of making polyhydric alcohol solutions of antiperspirant salts which are free of unbound water is described in U.S. Pat. No. 4,781,917. In that method, a powdered antiperspirant salt, which may be an enhanced efficacy salt, is dissolved in water (a 50% solution is exemplified), a polyhydric alcohol, such as propylene glycol, is added to the aqueous solution, then all of the water is removed by heating under vacuum. A method of making a propylene glycol solution of an aluminum-zirconium antiperspirant salt neutralized with zinc glycinate has also been described. An aqueous solution of aluminum chlorohydrate is refluxed in the presence of a small amount of propylene glycol, the solution is cooled to 70.degree. C., zirconyl hydroxychloride-gly is added, the solution is cooled to 40.degree. C., then zinc glycinate followed by propylene glycol is added. This solution is then distilled under vacuum to remove water, leaving a 30% by weight solution of antiperspirant active in propylene glycol.
The above-described methods suffer from a number of deficiencies. First, many of them are not efficient because they utilize a powdered material. Isolation of a powdered antiperspirant salt from solution is time consuming and costly. Second, it is believed that these methods will likely result in some loss of efficacy and/or will not provide clear solutions. Antiperspirant salts which have been obtained by spray drying are notoriously difficult to redissolve as clear solutions. Moreover, any method which requires an aqueous salt concentration over 20% will likely suffer some loss in efficacy.